MICROBES CAN MAKE
USEFUL PRODUCTS
WJEC Biology
Module 3
You will learn:
• What products are made by
microbes?
• What are the advantages of using
microbes?
• How is commercial production carried
out?
Learning outcomes
• To discuss the advantages of using
microbes in food production.
Time to Think
• how do we make use of microbes in
food production?
• gives examples of microbes used
• can you think of any advantages in
using micro-organisms in food
production?
Microbes in Food production
• Advantages of using microbes in food
production
– rapid growth
– contained growth so minimum space is
used
– predictable product is made under
controlled conditions
– they may grow on waste materials from
other processes.
Learning outcomes
• To understand how bacteria are used
in yoghurt production
Yoghurt Production
• Yoghurt is a thickened milk product with a
sour taste
• The sour taste is produced by bacteria
introduced into the milk which breakdown
lactose (milk sugar) to lactic acid.
• The low pH of lactic acid prevents other
microbes from growing in the milk.
• Yoghurt production is a batch process.
Yoghurt production
• 5 stages
– Pasteurisation
• Raw milk is pasteurised by heating the milk to 93oC, this
kills unwanted bacteria
– Cooling
– Incubation
• Bacterial culture is added to the cooled milk
– Chilling
• Temperature reduced to 5oC, reducing bacterial
enzyme activity
– Packaging
• Into sterile yoghurt pots, which are sealed and stored
below 4oC.
Incubation
• Streptococcus thermophilus and
Lactobacillus bulgaricus bacteria
convert milk sugar (lactose) into lactic
acid
• Optimum temperature 42oC
• The lactic acid produced lowers the
pH
• Milk protein coagulates (thickens)
• Process takes 4 – 6 hours
Flow diagram for the
manufacture of yoghurt
Bulk raw milk
Cool
Storage
4oC
pasteurisation
cooler
Packaging
Chiller 5oC
Incubation at
42oC for
6 – 8 hours
Quick Questions on Yoghurt
production
• At what temperature is the raw milk
pasteurised for yoghurt manufacture?
• If pasteurisation were not carried out,
what could happen to the yoghurt?
• Write a word equation for the
chemical reaction that causes the pH
of yoghurt to drop.
• Why should you remember Pasteur
when you drink milk or eat yoghurt?
Learning outcomes
• To understand how yeast is used in
baking
Yeast in Bread Making
• “strong flour” (flour with a high gluten
content) is used as this provides a
more stable loaf with even air pockets.
• Stages in bread production
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–
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–
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Activation
Kneading
Proving
Leavening
Baking
Activation
• Yeast is activated by adding warm
water and a little sugar
• Yeast respires aerobically and bubbles
of carbon dioxide form
Kneading
• Activated yeast is added to “strong
flour” to make dough.
• Dough is kneaded to
– distribute yeast evenly through the dough
– Remove most of the carbon dioxide
Proving
• Dough is put in a warm place
• Yeast respires anaerobically and
different enzymes in the yeast speed
up the breakdown of sugars to form
alcohol and carbon dioxide
• CO2 causes the volume to increase.
Reactions in Proving
yeast enzymes
Sugar + water
glucose + fructose
yeast enzymes
glucose + fructose
alcohol + carbon dioxide
Leavening
• Dough is kneaded for a second time
• Carbon dioxide produced is trapped
in the dough in small bubbles
• When the bubbles expand the volume
of the dough is increased.
• This gives the bread its light texture
Baking
• When the dough has doubled in
volume again, it is baked in a hot
oven.
• The high temperature denatures the
yeast enzymes stopping further
reactions.
• Alcohol evaporates and the carbon
dioxide bubbles expand.
Baking Questions
• What is the source of enzymes for
bread making?
• If a thermostat failure caused the
proving temperature to rise to 65oC in
a bakery, would you expect to get
“super-sized” loaves? Explain your
answer.
• What is the role of gluten protein in the
bread-making process?
Watching Dough rise
• Online resource
Learning outcomes
• to investigate factors affecting
fermentation in yeast
• to represent data collected in
appropriate tabular and graphic form
Fermentation in Yeast
• Yeast is a single-celled fungus
• Is reproduces asexually by budding
• Yeast can respire aerobically
Sugar + Oxygen  carbon dioxide + water
• Yeast can also respire anaerobically
Sugar  ethanol + carbon dioxide
• Anaerobic respiration produces less
cellular energy than aerobic.
Factors affecting fermentation
in yeast
• Sugar concentration
• Temperature
• pH
• Type of yeast
Learning outcomes
• To discuss the commercial production
of anti-biotics
Antibiotic Production
• Penicillin is a widely used anti-biotic,
first discovered by Alexander Fleming
in 1928.
• Large-scale production of penicillin
requires
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–
–
–
sterile conditions
Fermenter
Nutrient medium
Aeration with sterile air
Batch process in several stages
1. A sterile sample of Penicillium is added to
the culture medium
–
The sterile culture medium contains the
substances necessary for rapid growth of the
mould
•
•
•
•
–
Lactose
Amino acids
Mineral ions
Vitamins
pH and temperature are set at optimum levels
2. When Penicillium has used up the
nutrients it starts to produce penicillin
as a secondary product.
• The temperature is changed for this
stage
3. After about a week, the maximum
antibiotic concentration is reached
• Mould is filtered from the fermentation
liquid
• Antibiotic is separated from the liquid,
purified and crystalised
4. Antibiotic is processed into a form
where it is sold and used.
• All processes must take place under
sterile conditions
• Temperature must be controlled
throughout as penicillin can be easily
damaged by heat.
Fermenter
• A fermenter is a large steel vessel used
for biochemical reactions.
• Sensors monitor the conditions inside
• The sensors send information to a
computer, which then controls input
valves to maintain temperature, pH,
nutrient and oxygen levels at the
optimum value.
Learning outcomes
• To revise knowledge of enzyme action
• To understand the use of enzymes in
food production.
Industrial productions and the
use of enzymes
• Industrial application of enzymes
includes
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Food, wine and beer production
Making fructose sweeteners for soft drinks
Laundry detergents
Producing “stone washed” jeans
Manufacturing pharmaceuticals
Enzymes
• Enzymes are used in industry as they
bring about reactions at normal
temperatures and pressures which
would otherwise require expensive,
energy demanding equipment
• All enzyme reactions also give a pure
and reliable product.
• To produce enzymes, micro organisms
are cultured in a fermentation process
Enzymes in food production
• Early uses of enzymes in the food
industry include the production of
sweet syrups by breaking down starch.
– Carbohydrase and isomerase enzymes
are commonly used
Uses of enzymes in food
production
• Baby food
– Some baby food is pre-digested using
proteases so that the baby can use
amino acids without digestion
– Baby-milk powders are manufactured
from cows’ milk and are treated with
enzymes to break down the proteins
• This reduces the risk of allergic reactions
Fruit Juice production
• pectinases are used for extracting fruit
juice.
– Pectin in fruit holds the cellulose fibres in
the cell wall together
– The enzyme pectinase breaks down the
pectin and cell walls releasing the juice.
Pupil Activity
• Answer the exam question on
pectinase
• Complete the activity worksheet
analysing an experiment looking at the
effect of temperature on pectinase
action.
Learning outcomes
• to carry out at GCSE practical
examination on the extraction of fruit
juice using pectinase
Learning Outcomes
• To understand how biological washing
powders help to remove stains
Biological Washing Powders
• Modern biological washing powders
use enzymes that function efficiently at
low temperatures, this reduces fuel
costs.
• Food or biological stains include
– Fats and oils from fried items, butter or oily
dressings
– Protein from eggs, grass or blood
– Starches from sauces made with flour
Biological washing powders
• Biological washing powders have the
following enzymes added
– Lipase to breakdown fats
– Proteases to digest proteins
– Carbohydrases to remove starch stains
Biological powder advantages
• Improve stain removal
• Reduce costs
• Environmentally
– Biodegradable
• Enzymes are proteins and break down
naturally in the environment
– Energy efficiency
– Water efficiency
Pupil Activity
• The instructions on the box state that
biological washing powders are not
effective when used at temperatures
above 40oC
– Explain why this is so.
– If you had dropped fruit and cream down
the front of your best silk shirt, what would
be the advantage of using biological
washing powder?
Pupil Activity
• In the table write in whether you think
the benefits are for the
– Customer
– Environment
• Read through the handout and
answer the questions on Stone washed
jeans.